This invention relates to a TAB tape and a semiconductor device using the TAB tape, and more particularly to a TAB tape used as a tape-type Ball Grid Array (BGA).
FIG. 3 is a plan view, showing a conventional TAB tape of a three-layer structure. FIG. 4 is a cross sectional view, showing the TAB tape of FIG. 3. The TAB tape shown in FIGS. 3 and 4 comprises a resin tape 35 made of polyimide, an adhesive 34 coated on the resin tape, and copper foil patterns 31 and 32 formed on the adhesive. The copper foil patterns 31 and 32 consist of pads 31a to which solder balls are adhered, and leads 32a for connecting the pads 31a to a semiconductor chip (not shown). The copper foil patterns 31 and 32, the exposed portions of the adhesive 34 are coated with solder resist 33 which protects them. A hole is formed in the portion of the solder resist 33 which is located on each pad 31a. Supposing that each copper foil pattern has a film thickness of 18 .mu.m, the difference in level is also 18 .mu.m between the upper surface of each of the portions of the solder resist 35 which are coated on the copper foil patterns 31 and 32, and the upper surface of each of the portions of the solder resist 33 which are coated on the exposed portions of the adhesive 34.
FIG. 5 shows a stiffener, to which the polyimide tape 35 of the TAB tape is adhered. This stiffener is for a BGA tape, and comprises a metal plate 52 and an adhesive 51 coated thereon.
FIG. 6 is a view, useful in explaining a process for adhering the TAB tape shown in FIG. 4 to the stiffener shown in FIG. 5 by thermo-compression bonding. In FIG. 6, elements similar to those shown in FIGS. 4 and 5 are denoted by corresponding reference numerals, and no explanation is given thereof. As is shown in FIG. 6, the TAB tape and the stiffener are held between tools 61 and 62. In this state, pressure is applied to the TAB tape and the stiffener from the outside of both the tools 61 and 62, while heat is applied thereto. As a result, the tape and the stiffener are adhered to each other by means of the adhesive 51.
Thereafter, as shown in FIG. 7A, the resultant TAB tape 74 is adhered to a semiconductor chip 72, the chip 72 is sealed with a potting resin 71, and solder balls 75 are attached to the pads of the TAB tape 74, thereby forming a semiconductor device. FIG. 7B is a plan view of the semiconductor device shown in FIG. 7A.
In the FIG. 6 process for adhering the TAB tape to the stiffener by thermo-compression, the solder resist 33 has great irregularities as described above, and therefore the pressure from the upper and lower tools 61 and 62 does not reach the deep concave portions 63 of the solder resist. Accordingly, the adhesive 51 is not sufficiently pressed at locations below the concave portions 63, and hence may well have an insufficiently adhered portion 81 as shown in FIG. 8.
Thereafter, when the adhesive 51 is heated in a cure or reflow process, a bubble will occur at the insufficiently adhered portion. FIG. 9 is a sectional view, showing the state of the BGA tape in which a bubble 91 occurs therein. As is understood from FIG. 9, the BGA tape is warped due to the bubble 91, thereby degrading the flatness of the package, and it is difficult to make the lights the solder balls equal.